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Instructions

Specimens with hematocrit values greater than 55% must have anticoagulant adjusted. Specimens must be re-collected using a specified whole blood to sodium citrate ratio. Contact the performing Laboratory for specific instructions.

NOTE: REFRIGERATED specimens show a progressive decline in von Willebrand Factor Antigen over time. Therefore, results below the normal range, particularly if drawn from sites that routinely refrigerate specimens, should be interpreted in light of this effect.

Specimen Collection Criteria

Physician Office/Drawsite Specimen Preparation

For optimal results, maintain whole blood specimen at room temperature (20-25°C or 68-77°F) prior to transport. Transport whole blood to the Laboratory within 4 hours of collection. If transport within 4 hours is not possible, the following procedure must be followed for accurate results:

Centrifuge the capped tube at 1500 x g for 15 minutes.

Transfer plasma with a plastic pipette into a plastic polypropylene centrifuge tube, cap and centrifuge an additional 15 minutes at 1500 x g to obtain platelet poor plasma (PPP) which has a platelet count less than 10 bil/L. Plasma with a platelet count of less than 10 bil/L is critical for accurate results.

Immediately remove only the top two-thirds of the PPP and transfer it into a plastic tube.

Rejection Criteria

In-Lab Processing

Whole blood specimens must be processed as follows upon receipt in the Laboratory:

Centrifuge the capped tube at 1500 x g for 15 minutes.

Transfer plasma with a plastic pipette into a plastic polypropylene centrifuge tube, cap and centrifuge an additional 15 minutes at 1500 x g to obtain platelet poor plasma (PPP) which has a platelet count less than 10 bil/L. Plasma with a platelet count of less than 10 bil/L is critical for accurate results.

Immediately remove only the top two-thirds of the PPP and transfer it into a plastic tube.

Laboratory

Performed

Minimum once per week. Results available in 4-7 business days.

Reference Range

Normal Values: 60 - 150%.

Test Methodology

Change in Optical Absorbance (Siemens BCS).

Interpretation

Decreased values may be found in von Willebrand's disease. The presence of rheumatoid factor leads to a false high vWF level. vWF level increases during pregnancy, use of birth control pills, physical exercise and stress. Patients with type O blood type may have significantly lower vWF levels. This test may not detect the rare type 2 variants whose vWF Ag level is normal.

Clinical Utility

The comparison of factor VIII coagulation activity to von Willebrand factor is of value in differentiating von Willebrand's disease or hemophilia A and hemophilia A carriers.